Aside from its bark, humans can understand the intentions and feelings of their dogs through any number of different channels, whether it be the way they tilt their head, position their front legs, or, of course, frantically wag their tail. Most dog owners can pretty much read their canine companions like a book. It should come as no surprise, therefore, that the practice of cosmetic tail docking (or tail bobbing) has a profound effect on a dog's ability to communicate with other dogs. As the use of a robotic dog has shown, the lack of a long tail can seriously stunt your dog's social life.

Emily Anthes points this out in a recent PLOS article, where she says that not only is tail docking "a barbaric procedure in which several inches of a puppy's tail are amputated, often without anesthesia," it can also hamper its ability to convey its intentions to other dogs.

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Anthes reviews a remarkable study conducted by two biologists at Canada's University of Victoria that was published a while back in the journal Behavior.

To see if there were any potential behavioral anomalies caused by tail length, the researchers used a robotic dog that featured either a long or short tail, and they exposed this artificial impostor to 492 dogs at an off-leash park. In addition to the variable tail length, the robotic dog was made to either wag its tail or keep it stationary. Thus, there were four different conditions to chronicle. The researchers then studied and documented the various ways the leash-free dogs interacted with the robot.

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The first thing they noticed was that dogs who were smaller than the artificial version almost always approached it with caution. But as for dogs of equal or larger sizes, this is what they saw:

It was among the large dogs that the interesting behaviors emerged. These dogs were most likely to approach the robotic model when the robot had a long, moving tail. (They did so 91.4% of the time.) That makes sense, the researchers say. "Because the long tail was ﬂexible, the simulated motion appeared to us to resemble that of a loose, wagging tail of a real dog," they write. This kind of loose wag is often an invitation to play–and a social signal that the wagging dog means no harm.

On the other hand, a dog that is holding its tail perfectly still isn't giving off such obvious "come hither" signals, and large dogs approached the robot with a long, still tail significantly less frequently — only 74.4% of the time.

But when the researchers swapped the long tail for the short one, these preferences disappeared. Large dogs approached a short-tailed robot with a wagging tail just as often as one with a motionless tail (85.2% and 82.2% of the time, respectively). These findings suggest that the dogs were less able to discriminate between a tail that's wagging playfully and one that's standing still and erect when the tail itself is short. "It appears that the signals communicated by differences in tail motion were most effectively conveyed when the tail was long," the scientists write.

The large dogs were also twice as likely to pause while approaching the short-tailed models, perhaps using that time to try to decipher whether they should continue moving closer. As the researchers put it in their paper, "As the efficacy of a visual signal is related to its visibility … it may be that larger dogs had a harder time interpreting the ‘intentions' of the model when the tail was short."

In other words, the dogs were completely confused about the robotic dog's intentions. Consequently, dogs who have their tails bobbed are in a similar predicament — a condition that's likely introducing significant stress and uncertainty to their social lives.